Conventionally, there are devices known as projectors that project an image on a wall surface or a screen. The most common projectors are known as stationary projectors, which receive power from a utility power supply and are fixed to a predetermined position when they operate. Stationary projectors project, while they are fixed, an image onto a fixed position on a wall or a screen.
If a projector, which projects an image, is set in such a manner that the light emitting unit of the projector is not perfectly facing the projection surface, such as a wall or a screen, that is, the image is projected at a projection angle with the light emitting unit being tilted with respect to the projection surface, a trapezoidal image angled in accordance with the projection angle is displayed on the projection surface. For this reason, software-based keystone correction is performed.
A projector device is described in patent literature 1 that automatically corrects the position of the projector by using a tilt sensor. Moreover, a projector is described in patent literature 2 that calculates the tilt angle by using a computing unit and performs keystone correction by using a software-based keystone correcting unit.
Portable projectors have been proposed recently that are small and easy to carry. A mobile terminal with a projector function, for example, is described in patent literature 3. This mobile terminal includes an upper cabinet, a lower cabinet, a hinge member that rotatably joins the upper cabinet and the lower cabinet together, a lens, and a light source.